<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>let 命令-基本用法</title>

    <script>
        {
            var x = 20;
            let y = 10;
        }
        console.log(x);// 20
        console.log(y);//  ReferenceError: y is not defined
    </script>
</head>
<body></body>
</html>